This invention concerns improvements in or relating to vacuum metallising, in particular, to the metallising of the internal surfaces of hollow plastics articles such as the interior of tap knob bodies, control knobs, handles or the like.
It is already well known to employ vacuum metallising for coating the outside of plastics articles with metal elements such as aluminum, silver, gold etc. In the known process, the articles to be coated are placed in a vacuum chamber and the metal element is vaporized by electrical heating when the chamber is at high vacuum. The metal element is deposited on the outside of the articles due to the dispersion of the atoms of the vaporized metal. However, this process and apparatus cannot be used for internal surface coating because an even coating cannot be achieved, in particular on small surfaces like internal bores such as in tap bodies or control knobs.
Additionally, with small articles it is uneconomic to use a large vacuum chamber, despite multiple jig fixtures as there is substantial wastage of the metal element, which may be gold, and the pumping loads for inducing high vacuum are such as to lead to inefficient operation. Furthermore, there is always the necessity to batch up the articles for mounting on the jig, and this can interfere with efficient production rates.